Working up of chromium ores



Patented July 12, 1932 ERNST HAGKHOFER, 0F KREFELD-BOCKUM,

.POBATION or GERMANY OFFICE GERMANY, ASSIGNOR TO I. G. FARB'ENINV- Inus'rn'rn AKTIENGESELLSCHAFT, or FRANKFORT-ON-THE-MAIN, GERMANY, A con-WORKING U]? OF CHROMIUM ORES No Drawing. Application filed July-15,1929, Serial No. 878,589, and in Germany July 14, 1928.

p The invention relates to a preliminary treatment of chromium oresprior to the working up thereof.

I have found that chromium ore, which "is only diflicultly attackedbychemical agents, is converted into a condition in which it isconsiderably more readily amenable to chem-, ical attack by heating itin an oxidizing atmosphere to a temperature exceeding 800 C. The orethus treated can then be easily transformed by means of the knowndecomposition processes into chromium salts or chromates.

In conformity therewith I have found further that a chromium ore, whichhas been subjected to the said preliminary oxidizing treatment, whensubmitted to the known process of an oxidizing working up by means ofalkali carbonate in the, presence of lime, dolomite or bauxite yieldsalready at essentially lower temperatures the samedegree ofdecomposition as a non-pretreated ore at a higher temfor a short time inair, whereby the tempera sium nitrate.

ture minimum of 800 C. should not be lost sight of. The efiect of thepreliminarytreatment is assisted to a large extent, when the ore isheated in the presence of small amounts,

say, 2 to 3 percent of oxygen-yielding substances, such as for example,sodium or potas- For example, when subjecting a mixture of 7 parts ofuntreated chromium ore of 44% it will be found that after about an hour,

oxidized in one hour, while ore, treated as fully described inthepreceding paragraph gives a similar degree of decomposition andoxidation already after 30 to 40 minutes. 7

The improved process is likewise applicable to other decompositionprocesses than the lime soda'process and involves an essentialimprovementin the degree of decomposition and oxidation. For example,from a mixture consisting of 25 parts of chromium ore (44% 'Cr Ocontent), 25 parts of bauxite Al content) and-50 parts of sodiumcarbonate,56% of the ore contained therein is oxidized at 800 C. in thecourse of 50'minutes, while, after first igniting the ore for half anhour in the air at 1000 0., the degree of oxidation amounts to 71%. Iclaim:

1. Process which comprises heating chro-, mium ore in an oxidizingatmosphere to a temperature exceeding 800 C. in the-presence of a smallquantity of a solid oxidizing ma- 1 terial prior to subjecting it todecomposition in'accordance with the known processes. I

2. Process which comprises heating chro mium ore in an oxidizingatmosphere to a temperature exceeding 800 C. in the presence of 2percentof sodium nitrate prior to sub-- -j ecting it to decomposition inaccordance with the known processes.

In testimony whereof Ih'ave hereunto set I my hand.

' Cr O content, 6 parts of lime and 5 parts I of sodium carbonate tooxidation at 850 (1,

, ERNST ,HAGKHOFERQ; V

75-78% of the ore is oxidized. However,

when a mixture of the same composition, after having been previouslycalcined for about 30 minutes at about 1000 C. in the air,

is likewise oxidized at 850 C. 93-95% 'of the ore is converted intosodium chromate during the same time v a By employing higherdecomposition temperature' such as for example, 900 -1100 C. V

